1 fixed length array and variable length array

• Format of fixed length array definition:
  val arr = new Array[T] (array length)

• Variable length array definition format:
  val arr = ArrayBuffer[T]()
  Note that you need to import the package: import scala.collection.mutable.ArrayBuffer

• The code is as follows

import scala.collection.mutable.ArrayBuffer
object ArrayDemo{
	def main(args:Array[String]){
		//1. Initialize an 8-point fixed length array with all elements of 0
		//If it's new, it's the same as calling the apply method of an array to assign values to the array directly
		val arr1 = new Array[Int](8)
		//Print fixed length array directly, the content is the hashcode value of the array
		println(arr1)
		//By converting an array to an array buffer, you can see the contents of the original array
		//toBuffer converts an array to a variable length array buffer
		println(arr1.toBuffer)
	
		//2. The second method to define an array, direct assignment
		val arr2 = Array("hadoop","storm","spark")
		//Use () to access an element and print an element
		println(arr2(2))
	
		//The following is a variable length array
		val ab = ArrayBuffer[Int]()
		//Appends an element to the end of the array buffer, + = appends an element to the end
		ab += 1
		//Append multiple elements to the tail
		ab += (2,3,4,5)
		//Append an array++=
		ab ++= Array(6,7)
		//Append an array buffer
		ab ++= ArrayBuffer(8,9)

		//Insert the element at some position of the array, insert it from the subscript,
		//Insert - 1,0 from subscript 0
		ab.insert(0,-1,0)

		//remove the element at a certain position of the array, and delete it according to the subscript
		ab.remove(0)
		println(ab)
		
	}
}

2. Enhance for traversing arrays in Scala

• Enhance for loop traversal
• Use unitl to generate footmark, 0 unitl 10 contains 0 does not contain 10
  
• Code

object ForArrayDemo{
	def main(args:Array[String]){
		//1. Use enhanced for loop to traverse array
		val arr = Array(1,2,3,4,5,6,7,8,9)
		for(i <- arr)
			println(i)
		
		//2. Use until to generate a Range
		//The reverse method reverses the Range from which it was called
		for(i <- (0 until arr.length).reverse)
			println(arr(i))		
	}
}

3. Array conversion yield

• yield keyword can transform the original array, and a new array will be generated. The original array will remain unchanged
• Code

object ArrayYieldDemo{
	def main(args:Array[String]){
		//1. Define an array
		val arr = Array(1,2,3,4,5,6,7,8,9)
		//2. Multiply the even number by 10 to generate a new array
		val res = for(e <- arr if e % 2 == 0) yield e * 10
		println(res.toBuffer)
		
		//3. More advanced writing, more comfortable to use
		//Filter is a filter that receives a function with a return value of boolean
		//map is equivalent to taking out every element of the array and applying the function passed in
		val r = arr.filter(_ % 2 == 0).map(_ * 10)
		println(t.toBuffer)
	}
}

4. Algorithms commonly used in arrays